1. Field of the Invention
The present invention relates to a flow control device. It is particularly, but not exclusively, concerned with an adjustable flow control device which contains a plurality of orifices of varying diameter.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
There are many applications in the air and gas industry where a dependable and constant flow of air or gas is required. In particular, for twin tower pressure swing devices as used for compressed air drying and gas generation, a fixed orifice valve is particularly useful. An inherent part of such pressure swing devices is the use of a purge or re-generating stream of compressed air or gas from the high pressure ‘on-stream’ tower to the low pressure regenerating ‘off-stream’ tower. In all cases this purge air or gas effectively re-conditions the sorbent in the ‘off-stream’ tower.
The design of control valve arrangements on pressure swing devices varies considerably but in its simplest form, the tower switching is typically done using two shuttle valves and two exhaust valves which have proved both cost effective and extremely reliable. A variation on this valve arrangement is to use a shuttle valve for switching the inlet flow from one tower to the other and using two non-return valves for controlling the outlet flow of each tower. Non-return valves have the advantage of providing a means to prevent back flow through the pressure swing device which can cause severe damage to the sorbent. In such configurations the purge flow normally travels through a conduit in a by-pass arrangement circumnavigating the non-return valves however U.S. Pat. No. 8,262,784 and EP 2205339 describe a non-return valve with a single integral fixed orifice. The vast majority of such non-return valves are circular in design and are spring loaded in a normally closed position to prevent back-flow. However under normal process flow conditions the pressure differential across the valve forces the valve open to allow the process gas to pass downstream.
The proportion of purge flow to process flow is controlled by either an adjustable variable area flow control valve or a fixed orifice arrangement. Variable area control valves are relatively expensive and require a flow meter to set the correct proportion of purge flow furthermore they can be easily tampered with by unskilled operators causing the drier to work inefficiently. Although the use of fixed orifice valves is extremely useful and cost effective they also have a significant problem in that the orifice size is normally pre-set at the factory in line with a pre-ordered specification, and cannot easily be changed on site as generally a replacement serviceable component is required. Pressure swing devices have many variables affecting the required purge flow rate, for instance: change in pressure or temperature, change in process flow, change of required dew point, change of generated gas quality (i.e. purity of generated gas) and even change of altitude. It would therefore be extremely useful to have an adjustable flow control valve which could be easily and precisely adjusted to suit the conditions on-site.
One object of the present invention is to address the above problem.